(1) Field of the Invention
The instant invention relates to a method and apparatus for determining the irregularities in a surface of an article.
(2) Description of the Prior Art
In the manufacturing of various devices and parts, such as a head for an engine block, the part is predrilled and tapped to provide threaded holes for bolts for securing the part to another part. For example, threaded holes are drilled in the engine block so that the head can be secured thereto. After the predrilling and tapping operation, it is desirable to check each of the tapped holes to determine if the hole exists at all, whether the hole has been drilled to the proper depth, and whether or not the threads extend from the top of the hole to a predetermined depth thereof.
Devices have been constructed which include a probe having a fluid outlet and a back pressure sensor. The probe is inserted into the hole and the sensor detects increased back pressure within the probe caused by the absence of threads in the hole. These devices have been found to be ineffective in the workshop because unless the probe is specifically calibrated for a tight fit within the drilled hole, the back pressure differential between a threaded and nonthreaded hole is so small that the device cannot consistently differentiate therebetween.
The instant invention includes means for moving the probe between a neutral and a sensing position for increasing the pressure differential resulting between threaded and nonthreaded holes significantly, thereby solving
Prior art example devices for pneumatically gauging parts, and in some cases threaded bores, are shown in one or more of the following U.S. Pat. Nos:
2,846,871 Worthen August, 1958 PA0 2,889,704 Baker June, 1959 PA0 3,438,244 Plumpe April, 1969 PA0 3,494,078 Miyamoto February, 1970 PA0 3,608,356 Rozovsky September, 1971 PA0 3,792,605 Rabenau February, 1974 PA0 3,793,875 Jurkiewicz February, 1974 PA0 4,187,715 Nevitt February, 1980